Every employee in the country should automatically get set up with an IRA. Employers would be required to open an account if the new employee does not already have one. But if the employee does have one, the employer would direct money into that existing account.
A percentage of every employee's pay should automatically go into that IRA. From the first dollar we earn as teenagers, we should be forced to set aside a small percentage. We should have the option, like with a 401k, to say we want more to go into the account. The employer should have the option to match. And, like a traditional IRA, the employee should be able to put a certain amount of other money into it.
The key points: every employee must put at least, say, 2% of every paycheck into the account through their entire lives, and this is their one retirement account that they can use for everything. This would combine the IRA, 401(k), SIMPLE IRA, SEP IRA, etc.
If the employee wanted to have more than one IRA, they could. But their one account could also serve to hold money from all these different sources.
Maybe they would have two, one for pre-tax dollars and one for after-tax dollars (like a ROTH IRA).
This gives every employee a nest egg to watch grow. Easy options should be available (like in 401ks) and investments in things like "target funds" should be encouraged.
This is not meant to replace Social Security, it is meant to supplement it and to simplify the current dizzying array of IRA/retirement plan options and force everyone to do a bit to save.